Fluid distribution networks are used in a variety of applications to distribute fluid from a central reservoir to one or more remote locations where the fluid is available for use. Typically, one or more main transmission lines convey the fluid from the reservoir to one or more branch transmission lines that, in turn, convey the fluid to a respective one or more remote locations. Because most remote locations are designed to operate with a fluid having specific flow characteristics such as pressure and/or flow rate, the fluid-distribution network is designed to distribute more fluid than all the remote locations can simultaneously consume. Furthermore, the fluid distribution network is designed to provide the maximum amount of fluid at a pressure significantly higher than the highest design pressure of all the remote locations. Consequently, fluid-distribution networks typically include pressure-reducing valves to reduce the pressure and flow rate of the fluid before the fluid reaches the remote locations.
For example, a typical water-distribution system used by a city to supply water for commercial and residential use includes one or more main water lines that convey water from a local reservoir or pump station to zones within the city. Each zone typically includes a secondary water line that conveys the water from the main lines to neighborhoods within the zone. And each neighborhood typically includes a consumer distribution line that conveys the water from the secondary lines to the individual consumers within the neighborhood. The design pressure of the fluid received by the individual consumer is typically 40 pounds per square inch (psi) while the design pressure of the fluid in the main water lines is typically 300 psi. Consequently, pressure reducing valves are typically placed at the junctions of the main and secondary water lines and at the junctions of the secondary water lines and the consumer distribution lines. Pressure reducing valves, however, may also be placed within the main, secondary or consumer distribution lines.
FIG. 1 is a cut-away view of a conventional pressure reducing valve 10 incorporated in a typical fluid distribution network (omitted from FIG. 1 for clarity). The valve 10 includes an inlet portion 12 for receiving fluid having an inlet pressure, an outlet portion 14 for discharging fluid having a discharge pressure that is less than the inlet pressure, and a gate assembly 16 for regulating the amount of fluid allowed to flow from the inlet portion 12 to the outlet portion 14. The gate assembly 16 includes a piston 18 that can be moved relative to a piston seat 20 to increase or decrease the amount of fluid allowed to flow from the inlet portion 12 to the outlet portion 14. Even when the piston 18 is fully open, the amount of fluid allowed to flow into the outlet portion 14 is less than the amount of fluid that would normally flow through a transmission line without the valve 10. As the piston 18 closes, (moves toward the seat 20) the amount of fluid allowed to flow into the outlet portion 14 from the inlet portion 12 is reduced even further. Consequently, the valve 10 reduces the pressure of the fluid flowing out of the outlet portion 14 by reducing the amount of fluid flowing through the valve 10.
Because the valve 10 reduces the amount of fluid flowing from the inlet portion 12 to the outlet portion 14, the inlet pressure causes the flow velocity of the fluid flowing between the piston 18 and the piston seat 20 to increase with respect to the velocity of the fluid into the inlet portion 12. The flow velocity, and thus the flow energy of the fluid discharged from the outlet 14 is then reduced by turbulence that is generated within the flow as the fluid flows away from the valve 10, by changes in the direction of the flow as the fluid proceeds through the network, and by friction between the interior walls of the transmission lines and the fluid.
Unfortunately, reducing the flow velocity by these means does not allow one to capture the energy released from the flow in a readily usable form. If the fluid-distribution network includes many valves for reducing pressure, the total amount of energy released by the aggregate pressure reduction can be significant.
Thus, there is a need for a device that can reduce fluid pressure and use the released energy to generate power.